Near infrared (NIR) SPD is one of the key components for many applications such as quantum cryptography, optical network testing, semiconductor device analysis, three-dimensional imaging, eye-safe ranging and timing, etc. In optical communication, the wavelength of 1.55 μm is the most desirable for long-distance transmission, since optical fibers exhibit low dispersion and minimum loss (0.2 dB/km) at this wavelength. The most convenient detectors at 1.55 μm are based on InGaAs/InP APDs. APDs used as SPDs are referred to as single photon avalanche diodes (SPADs). SPADs have several advantages, they are compact, have lower operating voltages, cryogenic-free operation and also cost less.
In order to detect a single photon, commercial InGaAs/InP APDs designed for telecommunication applications are usually operated above the breakdown voltage (VBR) in the bi-stable mode. This mode of operation is referred to as the Geiger mode. In Geiger mode, an APD is able to sustain a large electric field across the junction. An incoming photon is absorbed and creates an electron-hole pair. The charge carriers are then swept through the junction and accelerated by the strong electric field. They can gain enough energy to generate secondary electron-hole pairs by impact ionization. These pairs are in turn accelerated and can generate new electron-hole pairs. If the electric field is high enough, impact ionization can yield a self-sustaining current pulse. This multiplication phenomenon is known as an avalanche.
During an avalanche event, some charge carriers created by the avalanche process can be trapped by defects in the SPAD's multiplication layer. If a trapped carrier is liberated during a subsequent gate pulse, it can trigger a new avalanche. Such an avalanche is called an after-pulse.
The after-pulse effect is one of the major bottlenecks limiting the performances of InGaAs/InP SPADs. Therefore, the InGaAs/InP APD is usually operated in gated Geiger mode in which the gate duration is generally set to a few nanoseconds. Then the interval between two consecutive gate pulses is set to more than the lifetime of the trapped carriers (several microseconds), which is very effective in lowering after-pulses. However, this mode allows operation at only megahertz rates; this has rendered InGaAs/InP APDs unsuitable for applications that require high-speed SPDs such as the high-speed clocked quantum key distribution (QKD) systems.
The after-pulse effect can be reduced also by selecting the operating conditions, in particular by decreasing the excess bias voltage and thus limiting the avalanche charges. However, this reduce the amplitude of the avalanche signal, makes it difficult to be discriminated from the APD capacitive response, especially when using fast gating signals.
A patent document 1 discloses a high-speed single-photon detector in telecommunication wavelength band. A DC bias voltage lower than the breakdown voltage is applied to an InGaAs/InP APD. A 500 MHz sine wave gating signal is superimposed with the DC bias voltage and applied to the APD so as to exceed the breakdown voltage by about 4V in a fractional time of each period. The sine wave gating signal passed through the APD is substantially completely removed by a filter, thereby improving signal to noise ratio and enabling to detect a single photon even if the avalanche multiplication time is shortened to reduce the after-pulse and the detection period. As a result, it achieves to detect a single photon in the 1550 nm communication band at a high speed.
A patent document 2 discloses a photon detection system including a photon detector configured to detect single photons, a signal divider to divide the output signal of the photon detector into a first part and a second part, wherein the first part is substantially identical to the second part, a delay mechanism to delay the second part with respect to the first part, and a combiner to combine the first and the delayed second part of the signal such that the delayed second part is used to cancel periodic variations in the first part of the output signal.
A patent document 3 discloses a photon detection system and a method of photon detection. A photon detection system, configured to determine the number of simultaneously detected photons in a pulse of radiation, comprises an APD, part to apply a bias across said photodiode and part to measure the size of an avalanche signal produced by illumination of the photodiode, wherein the avalanche signal is measured before the avalanche current through the photodiode has saturated. The photodiode may be operated in Geiger mode by applying a bias voltage greater than the breakdown voltage of the photodiode for a duration shorter than the time required for the avalanche current to saturate, or for a duration longer than this time in which case the avalanche signal is measured for a duration shorter than the time which the avalanche current take to saturate.
The non-patent document 1 reports an avalanche photodiodes and quenching circuits for single-photon detection. APDs operated above the breakdown voltage in Geiger mode and connected with avalanche-quenching circuits to detect single photons, and are therefore called single photon avalanche diodes (SPADs). Circuit configurations suitable for this mode of operation are critically analyzed and their relative merits in photon counting and timing applications are assessed. Although passive-quenching circuits (PQCs) are useful for SPAD device testing and selection, it has fairly limited applications. Suitably designed active-quenching circuits (AQCs) make it possible to exploit the best performance of SPADs. Thick silicon SPADs that operate at high voltages (250-450V) have photon detection efficiency higher than 50% from 540 to 850 nm wavelength and still ˜3% at 1064 nm. Thin silicon SPADs that operate at low voltages (10-50V) have 45% efficiency at 500 nm, declining to 10% at 830 nm and to as little as 0.1% at 1064 nm. The time resolution achieved in photon timing is 20 ps full width at half maximum (FWHM) with thin SPADs; it ranges from 350 to 150 ps FWHM with thick SPADs. The achieved minimum counting dead time and maximum counting rate are 40 ns and 10 Mcps with thick silicon SPADs, 10 ns and 40 Mcps with thin SPADs. Germanium and III-V compound semiconductor SPADs extend the range of photon-counting technique in the NIR region to at least 1600 nm wavelength.
The non-patent document 2 reports a balanced, gated-mode photon detector for quantum-bit discrimination at 1550 nm. A photon detector that combines two APDs has been demonstrated for quantum-bit discrimination at 1550 nm. Spikes accompanied by signals in a gated mode were canceled by balanced output from the two APDs. The spike cancellation enabled one to reduce the threshold in the discriminators and thus the gate pulse voltage. The dark count probability and after-pulse probability were reduced to 7×10−7 and 7×10−4, respectively, without affecting the detection efficiency equal to 11% at 178 K.
The non-patent document 3 reports a gated-mode single-photon detection at 1550 nm by discharge pulse counting. Gated-mode single photon detection using an APD is characterized by charge and discharge pulses, which are attributable to capacitive behavior. The discharge pulse rather than the photon-induced avalanche pulse is counted in single photon detection, in order to reduce after-pulses. The demonstration adopts an InGaAs/InP APD operating at 1550 nm. After-pulse probability per gate is evaluated at a repetition frequency of 5 MHz.
The non-patent document 4 reports a high performance of gated-mode single-photon detector at 1.55 μm. High performances of single photon detection at 1.55 μm were achieved by operating InGaAs/InP APDs in the gated-mode at the optimized temperature. As short pulses used in the gated-mode detection produce strong spikes, a transformer-based method was used to cancel the spikes, which makes it possible to reduce the dark counts by using short-gate pulse durations, and to discriminate the avalanche signals at low thresholds. The spike-cancellation single photon detection at the optimized temperature produced a detection efficiency of 20% with a dark-count probability of 3.4×10−7 per pulse. With such a SPD, a stable single photon routing was realized in 155 km optical fibers with an average photon number equal to 0.1 photons/pulse, exhibiting a fringe contrast of 87%.
The non-patent document 5 reports a high-speed InGaAs/InP-based single-photon detector with high efficiency. An efficient SPD at telecom wavelength of 1.55 μm was realized with an InGaAs/InP APD at −30° C. By implementing a short gating pulse and optimizing the self-differencing circuit, a detection efficiency of 29.3% was achieved with an error count probability of 6% at the gating frequency of 200 MHz, paving the way for the high-efficiency and low-noise fast detection of the NIR single photons.
The non-patent document 6 reports a 1.5 GHz single-photon detection at telecommunication wavelengths using sinusoidally gated InGaAs/InP avalanche photodiode. The SPD is based on a sinusoidally gated InGaAs/InP APD. The gate repetition frequency of the SPD reached 1.5 GHz. A quantum efficiency of 10.8% at 1550 nm was obtained with a dark count probability per gate of 6.3×10−7 and an after-pulse probability of 2.8%. Moreover, the maximum detection rate of the detector is 20 MHz.
The non-patent document 7 reports a multi-gigahertz operation of photon counting InGaAs avalanche photodiodes. An InGaAs/InP APD is operated at 2 GHz for efficient single photon detection at telecom wavelengths. Employing a self-differencing circuit that incorporates tuneability in both frequency and arm balancing, extremely weak avalanches can now be sensed so as to suppress after-pulses. The after-pulse probability is characterized as 4.84% and 1.42% for a photon detection efficiency of 23.5% and 11.8%, respectively. The device will further increase the secure bit rate for fiber wavelength quantum key distribution.
Patent document 1: US 2009/0039237 A1
Patent document 2: US 2010/0111305 A1
Patent document 3: GB 2456149 A
Non-patent document 1: S. Cova, M. Ghioni, A. Lacaita, C. Samori, and F. Zappa, “Avalanche photodiodes and quenching circuits for single-photon detection”, Appl. Opt., vol. 35 no. 12, pp. 1956-1976, 1996.
Non-patent document 2: A. Tomita, and K. Nakamura, “Balanced, gated-mode photon detector for quantum-bit discrimination at 1550 nm”, Opt. Lett., vol. 27 no. 20, pp. 1827-1829, 2002.
Non-patent document 3: A. Yoshizawa, R. Kaji, and H. Tsuchida, “Gated-mode single-photon detection at 1550 nm by discharge pulse counting”, Appl. Phys. Lett., vol. 84 no. 18, pp. 3606-3608, 2004.
Non-patent document 4: G. Wu, C. Zhou, X. Chen, and H. Zeng, “High performance of gated-mode single-photon detector at 1.55 μm”, Opt. Com. Vol. 265, pp. 126-131, 2006.
Non-patent document 5: L. Xu, E Wu, X. Gu, Y. Jian, G. Wu, and H. Zeng, “High-speed InGaAs/InP-based single-photon detector with high efficiency”, Appl. Phys. Lett., vol. 94, pp. 161106, 2009.
Non-patent document 6: N. Namekata, S. Adachi, and S. Inoue, “1.5 GHz single-photon detection at telecommunication wavelengths using sinusoidally gated InGaAs/InP avalanche photodiode”, Opt. Express, vol. 17 no. 8, pp. 6275-6282, 2009.
Non-patent document 7: Z. L. Yuan, A. W. Sharpe, J. F. Dynes, and A. R. Shields, “Multi-gigahertz operation of photon counting InGaAs avalanche photodiodes”, Appl. Phys. Lett., vol. 96, pp. 071101, 2010.